Path: utzoo!attcan!uunet!tut.cis.ohio-state.edu!rutgers!ucsd!ogicse!sopwith!snoopy
From: snoopy@sopwith (Snoopy)
Newsgroups: sci.electronics
Subject: Re: UPS
Message-ID: <1990Jul29.001243.22571@sopwith>
Date: 29 Jul 90 00:12:43 GMT
References: <7TuPm1w162w@zl2tnm.gp.govt.nz>
Reply-To: snoopy@sopwith.UUCP (Snoopy)
Organization: The Daisy Hill Puppy Farm
Lines: 51

In article <7TuPm1w162w@zl2tnm.gp.govt.nz> don@zl2tnm.gp.govt.nz (Don Stokes) writes:
|>From: shenkin@cunixf.cc.columbia.edu (Peter S. Shenkin)

|> I'm trying to sort through the maze of vendors' claims in order to pick
|> a UPS

I'm also shopping for a UPS.  Some of these claims appear to conflict.

|> So my SECOND QUESTION is whether the ballast route to making a unit "on-line"
|> as "good" as the inverter-always-on route?  That is, perhaps instead of
|> a two way classification (standby and on-line), we should have a three-way
|> classification:
|
| Maybe; depends a lot on the quality of the unit.  It still isn't a true
| online UPS; what you've got in the "balasted standby" is a power
| conditioner of sorts with a battery, and must be treated as such.

Best claims that their units will supply power without a glitch when
the power goes out.  American Power Conversion Corp. claims that this
is only true in a pull-the-plug test.  In a normal power outage, the
unit is still connected to other loads through the building wiring,
and APC claims that the other loads will suck the power out of the ferro
transformer before the unit can disconnect itself.  Best shows a scope
photo to support their claim, but doesn't specify if this is a pull-the-plug
test or a leave-it-connected-to-other-loads-through-the-building-wiring test.
Interestingly, APC provides a bunch of scope photos showing what happens
to various units during a blackout, but they don't include Best.

Does anyone know which claim is correct?

Another question is: in the case that commercial power comes back before
the batteries run out, does the Best unit sync itself up with commercial
power when the commercial power comes back, to avoid glitches (or worse!)
from connecting two out-of-phase sources of AC together?

*If* the Best unit doesn't glitch on either power-down or power-up,
I see no advantages and some disadvantages (MTBF, inefficiency)
to the double-conversion units.

In the case that power doesn't come back in time, can these units
be setup to wait for the batteries to recharge before starting the
computer back up?  A UPS with dead batteries isn't a UPS.

And lastly, is one stuck paying list price for these things, or are
discounts available?

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